Figure provided by Dr. Shyril O’Steen.
Venetoclax is a small molecule drug inhibiting the anti-apoptotic activity of BCL-2 protein, overexpressed in several cancers including B-cell type of Non-Hodgkin Lymphoma (B-NHL). This drug was evaluated in clinical trials to treat several types of lymphomas resulting in its FDA approval for the treatment of chronic lymphocytic leukemia. However, venetoclax has not been curative as a single agent. Combination of venetoclax with other treatments that could benefit from its pro-apoptotic effects, represents an appealing strategy to increase treatment efficiency. As such, radiation therapy that induces DNA damage and requires apoptosis activity for anti-lymphoma activity represents a good candidate. To test this hypothesis Drs. Shyril O’Steen and Oliver Press (Clinical Research Division) have evaluated venetoclax administration either alone or in combination with beam radiation therapy or radioimmunotherapy (coupling of antibodies and radionuclides to specifically target and deliver the DNA damaging molecules to cancer cells) for the treatment of Non-Hodgkin Lymphoma (NHL). “BCL-2 pathway has additional proteins that block apoptosis, such as BCL-XL, that are also often overexpressed and so might prevent apoptosis even when venetoclax has blocked BCL-2. And of course all cancer treatments create strong pressure favoring the evolution of resistant clones. Attacking with multiple therapies improves the odds of eradicating all cells, not leaving anyone behind harboring a resistance factor”, explained Dr. O’Steen. Results of the study were recently published in Cancer Research journal.
Combination of venetoclax with radiotherapy was first assessed in vitro using 14 different cell lines derived from patients suffering from NHL and representing five types of lymphoma. In 10 of these cell lines, combination of venetoclax with external radiation synergized and increased cell death. Sensitivity to venetoclax as a single agent was generally predictive of the combination efficiency. Additionally, flow cytometric analysis of the expression levels of BCL-2, BCL-XL or MCL-1, known as proteins involved in the Bcl2 pathway, indicated that lower expression of BCL-XL improved efficiency of the combination treatment.
Further evaluation was carried out in vivo. To this end, immunodeficient mice were engrafted with NHL cell lines (xenograft) to develop the tumors to target. These cell lines were selected based on their diversity representing different types of NHL and various sensitivities to venetoclax as determined earlier in the study. Mice were injected with these cells and irradiated 8 to 16 days later (depending on the tumor development). Venetoclax treatment was initiated one day later and administered orally once a day for 10 to 28 days.
Venetoclax administered as a single agent did not have a significant impact on the survival while combination with external radiation showed the best survival relative to single agent therapies in mice. This was observed with two different NHL cell lines that showed low and intermediate sensitivities to combination therapies in vitro and suggested that this combination might prove efficient even for lymphoma initially resistant to venetoclax as a single agent.
The researchers also investigated the combination of venetoclax with radioimmunotherapy. Antibodies were administered first, followed by administration of a clearing agent one day later to eliminate any unbound antibodies before injection of the radionuclide compound 90Y-DOTA. Two days following this final injection the venetoclax treatment was initiated. Again, combination treatments were significantly more efficient than single agents. This was observed with two different NHL cell lines. Tumors developed from the U2932 NHL cells, that showed the highest sensitivity to combination treatment in vitro, also showed higher sensitivity to the combination treatment in vivo. Additionally, mice survival reached 100% with this combination. Interestingly, U2932 also expressed less BCL-XL, in accordance with the in vitro observation that lower BCL-XL expression increase combination treatment efficiency.
No toxicity was observed in treated mice with venetoclax only, which is already FDA approved. Radiation therapy and radioimmunotherapies as single agents led to transient weight loss followed by a full recovery within several days. Encouragingly, no additional effects were observed when combining venetoclax and radiation therapies. These results are promising as they show for the first time that the rationale combination of an anti-apoptotic drug inhibitor with radiation therapy causing DNA damage represents a safe and promising new treatment option for Non-Hogdkin lymphoma. Dr. O’Steen concluded: “Pretargeted radioimmunotherapy is an exciting tool for treating leukemia and lymphoma. We’re looking forward to combining additional novel agents with PRIT, and seeking factors measurable in patients that predict success”.
Funding for this study was provided by the National Institute of Health (NIH), the Fred Hutchinson Cancer Center support grant and by the David and Patricia Giuliani Family Foundation.
O’Steen S, Green DJ, Gopal AK, Orozco JJ, Kenoyer AL, Lin Y, Wilbur DS, Hamlin DK, Fisher DR, Hylarides MD, Gooley TA, Waltman A, Till BG, Press OW. 2017. Venetoclax synergizes with radiotherapy treatment of B cell lymphomas. Cancer Research.